A new study on how design and planning can keep these numbers down. (Photo: Amy the Nurse via Flickr)

How the heck can we get people to drive less?

That’s one of the most vexing questions facing sustainable transportation advocates. Higher gas prices seem to do the trick, although anecdotal evidence suggests that watching an entire ecosystem being destroyed by a busted oil well doesn’t have much effect.

The fact is, too often we are engaging in guesswork and speculation when we talk about strategies to reduce vehicle miles traveled (VMT). But thanks to a new study of how land use affects transportation choices, we now have a great new source of actual data. The study, a meta-analysis of 50 previous studies, is called "Travel and the Built Environment," and it’s published in the Summer 2010 issue of the Journal of the American Planning Association. It’s the result of several years’ work by Reid Ewing of the University of Utah and Robert Cervero of the University of California, Berkeley.

What they found: location matters most when it comes to land use, driving and the environment.

The study’s key conclusion is that destination accessibility is by far the most important land use factor in determining a household or person’s amount of driving. To explain, ‘destination accessibility’ is a technical term that describes a given location’s distance from common trip destinations (and origins). It almost always favors central locations within a region; the closer a house, neighborhood or office is to downtown, the better its accessibility and the lower its rate of driving. The authors found that such locations can be almost as significant in reducing driving rates as other significant factors (e.g., neighborhood density, mixed land use, street design) combined.

Daniel Nairn at Discovering Urbanism also wrote about the study, pulling out a thread about connectivity on the street-grid level:

[The study is a] big win for connectivity, which is great because this is something that can actually be done. Some cities and states are starting to write codes to ensure a robust street network in new developments. Even more important is retrofitting connections into existing networks. Hopefully these results will spur localities to look for those odd scraps of land and consider punching a street or multi-use trail through them. Although cycling was not considered in this analysis, I can attest from personal experience that street connectivity is the single most important factor for enhancing safety and convenience.

More excellent analysis, focusing on the importance of intersection density, can be found at Lawrence Aurbach’s Ped Shed.

More from around the network: Livin in the Bike Lane on the effect of air pollution on bicyclists (this is not good news, folks). On Two Wheels wonders if Montréal could benefit from fewer traffic signs. And The Bellows considers the benefits of congestion.

“the study’s key conclusion is that destination accessibility is by far the most important land use factor in determining a household or person’s amount of driving.”

We needed a study for this?

thedavidmo

“To explain, ‘destination accessibility’ is a technical term that describes a given location’s distance from common trip destinations (and origins). It almost always favors central locations within a region; the closer a house, neighborhood or office is to downtown, the better its accessibility and the lower its rate of driving.”

In other words, the single most effective thing we can do to decrease the rate of driving is to relax zoning regulations and allow an increase in population density, especially nearer to downtown…the dreaded “Manhattanization” of SF. A lot of people get upset when giant residential skyscrapers are built, but from a transit perspective it’s way better for all those people to be located in a single building close to the city center than sprawled out all over the city/adjacent regions.

http://ridinginriverside.blogspot.com Justin N

I agree with thedavidmo in part, and disagree in part. Density is generally a good thing, yes, but I’m not sure if we need to open up zoning restrictions in places like San Fransico, where there is already enough density to support a robust transit, cycling and walking culture. “Car-free Cities” finds that the critical density to support transit, and therefore cycling and walking, is development around 3-4 stories, and many historical rowhouse neighbourhoods are dense, walkable and transit-friendly. What is needed is not the further densification of places like SF, which are already dense, but the densification of the suburbs. We need to be bulldozing housing tracts and strip malls and building 3-4 story human-scale development where they once stood. Doing this will get more cars off the road, and get more people on buses, bikes and sidewalks, than will super-dense Manhattan-style development. It’s time to loosen zoning density restrictions, to be sure, but not in the cities- in the suburbs.

http://blogbilongadam.blogspot.com Adam Villani

“It almost always favors central locations within a region; the closer a house, neighborhood or office is to downtown, the better its accessibility and the lower its rate of driving.”

… which is why supposed “New Urbanist” developments built on greenfields at the edge of suburbia are really just suburban developments dressed in urbanist drag.

“I’m not sure if we need to open up zoning restrictions in places like San Fransico, where there is already enough density to support a robust transit, cycling and walking culture.”

Good point about SF already being dense enough to support a non-auto-dependent culture; I think the stronger argument for more density in SF is that restricting the supply of housing had made it unaffordable for working-class people.

“connectivity on the street-grid level”

I wonder about connectivity at the freeway-grid level. Might finishing the gap in Interstate 710 actually decrease VMT and vehicle pollution, particularly from idling in traffic?

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